1. Field of the Invention
The present invention relates to a battery charger configured to be connected to an external battery by way of external battery cables and more particularly to a battery charger with automatic voltage detection which automatically determines the nominal voltage of the battery connected to its battery charger terminals and charges the battery as a function of the detected nominal voltage irrespective of the nominal voltage selected by a user.
2. Description of the Prior Art
Various battery chargers for charging different types of batteries are known in the art. Examples of such battery chargers are disclosed in U.S. Pat. Nos. 5,729,115; 6,384,575; 6,625,477; and 7,468,596. Such a battery charger is also disclosed in US Patent Application Publication No. US 2007/0247105 A1, all hereby incorporated by reference.
Since each different type of battery needs to be charged according to a specific charging algorithm for the specific battery, it is necessary for the battery charger to be properly configured for the battery type and nominal voltage of the battery connected to its battery charger terminals. Some known battery chargers require the user to determine the battery type and nominal voltage of a battery connected to its battery charger terminals. Such battery chargers require the user to manually configure the battery charger. Other known battery chargers automatically determine the battery type and the nominal voltage of the battery connected to its battery charger terminals and automatically configure the battery charger.
Various techniques are known for battery chargers for automatically determining the nominal voltage of the battery connected to the battery charger. For example, U.S. Pat. Nos. 6,384,575; 6,384,575 and US Patent Application Publication No. US 2007/0247105 A1 all disclose battery chargers which distinguish different types of batteries by size. In general, these battery chargers include multiple charging pockets. The pockets are configured to receive different size batteries with different nominal voltages. These chargers merely need to sense which pocket has a battery connected to it in order to determine the battery voltage. However, such a technique is not applicable to battery chargers that are configured to be connected to external batteries by way of external battery cables.
U.S. Pat. No. 6,625,477 discloses a different technique for determining the nominal voltage of a battery connected to its battery charger terminals. The battery charger disclosed in the '477 patent is configured to identify the nominal voltage of specially configured batteries which include an identification contact. The battery charger includes a plurality of tap voltages juxtaposed so that when the battery is received in the battery charger, the identification contact on the battery will be connected to a tap voltage depending on its size and thus nominal voltage. Again, such a technique is not applicable to battery chargers that are configured to be connected to external batteries by way of external battery cables.
U.S. Pat. No. 5,729,115 discloses yet another technique for determining the nominal voltage of a battery connected to its battery charger terminals. In this technique, the battery charger includes a sensing contact in addition to the positive and negative battery terminals. The sensing contact is juxtaposed adjacent to the positive battery charger terminal. Whenever a battery is inserted into the battery charger, the sensing contact is configured so that it will be in contact with the positive battery terminal for a first type of battery and will not be in contact with the positive battery terminal for a second type of battery. The battery charger senses the voltage at the sensing contact and makes a determination of the nominal voltage of the battery connected to its positive and negative terminals based on the voltage at the sensing contact. This technique, like the techniques discussed above, is not applicable to battery chargers that are configured to be connected to external batteries by way of external battery cables.
Thus, there is a need for a battery charger that is configured to be connected to an external battery by way of external cables that can automatically determine the nominal voltage of the battery connected to its battery charger terminals.